Structures

C structures are special, large variables which contain several named variables inside. Structures are the basic foundation for objects and classes in C. Structures are used for:

Serialization of data
Passing multiple arguments in and out of functions through a single argument
SData structures such as linked lists, binary trees, and more

The most basic example of structures are points, which are a single entity that contains two variables - x and y. Let's define a point:

    struct point {
        int x;
        int y;
    };

Now, let's define a new point, and use it. Assume the function draw receives a point and draws it on a screen. Without structs, using it would require two arguments - each for every coordinate:

    /* draws a point at 10, 5 */
    int x = 10;
    int y = 5;
    draw(x, y);

Using structs, we can pass a point argument:

    /* draws a point at 10, 5 */
    struct point p;
    p.x = 10;
    p.y = 5;
    draw(p);


                            

To access the point's variables, we use the dot . operator.

Typedefs

Typedefs allow us to define types with a different name - which can come in handy when dealing with structs and pointers. In this case, we'd want to get rid of the long definition of a point structure. We can use the following syntax to remove the struct keyword from each time we want to define a new point:

    typedef struct {
        int x;
        int y;
    } point;

This will allow us to define a new point like this:


    point p;

Structures can also hold pointers - which allows them to hold strings, or pointers to other structures as well - which is their real power. For example, we can define a vehicle structure in the following manner:

    typedef struct {
        char * brand;
        int model;
    } vehicle;

Since brand is a char pointer, the vehicle type can contain a string (which, in this case, indicates the brand of the vehicle).

    vehicle mycar;
    mycar.brand = "Ford";
    mycar.model = 2007;